1. Field of the Invention
The present invention relates to audio systems and speakers. More particularly, the invention relates to an improved sound transducer for imparting acoustical energy directly to a solid surface such as a wall or pane of glass.
2. Description of the Prior Art
High performance audio systems and speakers continue to grow in popularity as more and more consumers install home theater systems in their homes, offices and other personal spaces. Such home theater systems typically consist of a high definition TV, projection TV, plasma screen, or other monitor; one or more video sources such as a DVD player or a VCR; a surround-sound receiver; and a plurality of speakers coupled with and driven by the surround-sound receiver.
High performance surround-sound receivers typically have five or seven separate audio channels for driving five or more speakers. The speakers are strategically positioned around a listening area to accurately produce the audio portion of a movie or other program. A pair of speakers may, for example, be positioned behind a typical listening area, another pair of speakers may be positioned in front of the listening area, and another pair of speakers may be positioned to the sides of the listening area.
Speakers convert electrical energy representative of music or other sounds to acoustical energy. Conventional speakers include a voice coil which moves relative to a permanent magnet when it receives an alternating audio signal. The voice coil then vibrates a paper diaphragm or cone to provide sound waves. The cone moves because of a dynamic interaction between two magnet fields, one coming from the permanent magnet and the other created by the signal voltage applied to the voice coil. The permanent magnet's field does not change direction; it remains highly concentrated and constant near the voice coil. An alternating audio signal applied to the voice coil creates an alternating magnetic field emanating from the voice coil. The alternating magnetic field of the voice coil interacts with the stationary magnetic field of the permanent magnet to move the voice coil. Specifically, the voice coil and the attached cone move forward and backward in accordance with the varying polarity of the signal applied to the voice coil. The oscillations of the diaphragm closely follow the variations in the applied electrical signal to set up sound waves.
Because conventional speakers rely upon the movement of a diaphragm or cone, they must be mounted so that the diaphragm is at least partially exposed to the listening area in which the sound is directed. Mounting numerous speakers in a listening area without interfering with windows, doors, columns, and other structural components of a room can be challenging. One way to overcome this challenge is to hang some or all of the speakers from the room's ceiling with swiveling brackets so they may be oriented to project sound in desired directions. However, some people find this mounting arrangement unsightly, especially when numerous speakers of varying sizes must be hung from the ceiling. Another installation method flush mounts the speakers in walls, ceilings and other surfaces so that the speakers do not project as far into a room. However, this method is considered unattractive by some people as well, because the speakers and their associated grills take up valuable wall and ceiling space and remain visible, thus detracting from the appearance of the room.
Magnetostrictive speakers, such as the SolidDrive™ speakers sold by Induction Dynamics® have been developed to alleviate some of the problems associated with speaker installation. Such speakers convert audio signals to powerful vibrations that can be transferred into solid surfaces such as walls, ceilings, windows, tables, office desks, etc., thus delivering sound from the entire surfaces. This permits the speakers to be positioned entirely behind these surfaces and therefore completely hidden from view. For example, such speakers are often mounted behind walls so that there are absolutely no visible speakers or wires. Although magnetostrictive speakers can be hidden and therefore solve many of the installation problems discussed above, they do not reproduce sound as accurately as conventional speakers and often exhibit non-uniform and less predictable frequency responses.
Sound transducers which use conventional voice coil technology to impart acoustical energy to solid surfaces have also been developed. However, these prior art sound transducers are generally not powerful enough to move a rigid wall or other solid surface sufficiently to create a desirable level and quality of sound. Moreover, such prior art transducers do not produce a uniform frequency response due to their construction.